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Copolymers and blends of polyhedral oligomeric silsesquioxane (POSS) and polyimides have been shown to resist atomic-oxygen (AO) attack, making them promising candidates as space-durable materials in the harsh oxidizing environment of low Earth orbit (LEO). CORIN® is a commercially available and colorless POSS–polyimide which has the desirable but uncommon property among polyimides that it may be dissolved in a solvent and applied at room temperature, thus making it possible to have a widely applicable clear coating for protection from AO in LEO. The physical properties of CORIN® have been largely characterized, but its AO resistance has received limited study. We have thus used a hyperthermal AO beam to expose CORIN® and other POSS-containing polyimides, 7.3 wt% and 9.1 wt% Si7O9 trisilanolphenyl POSS blended with poly(pyromellitic dianhydride-co-4,4′-oxydianiline), to characterize their resistance to AO attack. CORIN® was found to have a particularly low erosion yield that is ≲1% that of the ubiquitous satellite material, Kapton, which agrees favorably with a result from an experiment on the International Space Station. The other POSS-containing polymers exhibited somewhat higher erosion yields of 1.4 and 2.2% that of Kapton, respectively. Surface characterization of CORIN® showed that it remained relatively smooth during AO exposure and implied that a passivating silicon oxide was formed. The comparison of the AO effects on CORIN® and the other POSS–polyimides suggests that the net effect of AO on such POSS–polyimides depends on the density of Si atoms as well as the reactivity of the organic component of the polymer. This work adds to our confidence in the use of POSS-containing polymers in LEO and, especially, in very LEO, where the necessity of protecting satellite materials and components from AO attack is critical. [ABSTRACT FROM AUTHOR]

Relying on the demands of Internet of things application,a detailed review on the status quo of LEO (low earth orbit) satellite communication system was given,and the components of communication system were compared and explained separately.Afterwards,the characteristics of the NB-IoT land-based communication network widely applied at present and existing LEO satellite communication system were compared,and a feasible design scheme for IoT-oriented LEO satellite system was provided,and its main parameters and characteristics were briefly described.

The space environment consists of various complex phenomena, which could have a strong influence on the spacecraft operation in different aspects. Since the very beginning of space exploration, numerous studies have been done on the space environment. However, most of the existing literature focuses on the investigation of the details of environmental phenomena, while the space environment has rarely been discussed from the perspective of orbits types. Therefore, a comprehensive review on analyzing and comparing the environmental characteristics among diverse orbits in space is of great significance. In this paper, the main components of the space environment are introduced, including the neutral atmosphere, the plasma environment, the radiation environment, the macroscopic particle environment, the geomagnetic field, the temperature field, and the solar activities. The relations of the various space environmental components are also discussed. The dominant environmental components and their effects on spacecraft in different orbits, i.e., the geosynchronous orbit (GEO), the low earth orbit (LEO), the medium earth orbit (MEO), and the high earth orbit (HEO), are investigated, respectively. The space environment that should be taken into particular consideration is summed up to facilitate the design of the spacecraft in a specific orbit.

The regional navigation satellite system (RNSS) is recently used in some countries to cover or enhance their local navigation. The most important satellite navigation systems to date are in the Earth medium orbit (MEO) and Earth synchronous Earth orbit (GEO), which are characterized by big satellites, and high launch, construction, and operation costs. In contrast, low Earth orbit (LEO) small-satellite constellations have recently become attractive because of their advantages, such as a significant reduction in system cost, an increase in communication volume, and a reduction in latency. Therefore, in this study, the spatial geometry of a LEO constellation is designed for Iran to increase the required regional navigation performance. For this purpose, the optimal constellation configuration is obtained through a multi-objective genetic algorithm (MOGA) utilizing a cost function with a combination of the geometry dilution of precision (GDOP), the number of satellites, and orbital height in the form of a design procedure. Moreover, reducing the feasible region of longitude of the ascending nodes of orbit planes is applied in the design process to reduce the search space. The simulation results indicate the constellation designed performance.

The variable electromagnetic environment in geospace plays a crucial role in influencing the occurrence probability of satellite anomalies. FORMOSAT-3 (FS3) is a Low-Earth-Orbit (LEO) mission, which consists of six identical microsatellites that orbit in the altitude of 700–800 km and with an inclination of 72°. The dependences of the FS3 satellite anomalies on space weather conditions have not been investigated in the past. With an exception of a small number of extremely high geomagnetic events, we find that the occurrence rate of the FS3 anomalies is negatively correlated with the level of geomagnetic activity. Moreover, the relationship between numbers of anomalies and sunspots is also anti-correlated. A superposed epoch analysis demonstrates that the intensity of galactic cosmic rays (GCR) is relatively high at the times of the anomalies. All these results infer that the FS3 anomalies predominantly occurred under the conditions associated with low solar activity. The possible main cause for the FS3 anomalies is high-energy trapped protons or GCR. In summary, this paper presents a statistical result that a satellite can be prone to suffer an anomaly under low solar or geomagnetic activity. [ABSTRACT FROM AUTHOR]

Space weather is driven and modulated by the activity in the Sun. Space weather events have the potential to inflict critical damage to space systems. Nowadays, space assets are essential in our basic needs, such as communications, cell phone networks, navigation systems, television and internet. Hence, understanding space weather dynamics and its effects on spacecraft is crucial for satellites engineers and satellite operators, in order to prevent and mitigate its impacts. In the last decade our Sun has erupted several times causing dozens of space weather events. Some of these led to satellite malfunctions and outages lasting from mere hours, up to days and weeks. This research is focused on two different space weather events, March 7–8, 2012, and September 6–10, 2017, that occurred during the last ten years and caused satellite anomalies that are related to an increase in the single event upsets rate. Single event upset is a bit flip in a memory device due to high energy particle interaction with the device sensitive volume. During these two periods, Eros B, a low Earth orbiting polar satellite detected an increased rate of single event upsets on two of its processing computers when the high energy proton flux was elevated. On both occasions X-class flares were detected, and the increased single event upsets count rate in Eros B took place only after the 100 MeV protons flux was three orders of magnitude above the background levels. In this research, Israeli satellite anomalies that were detected are first demonstrated. [ABSTRACT FROM AUTHOR]

Color filters and conductive films are widely used in spacecraft, while the lack of lightweight, flexibility, and atomic oxygen (AO) durability confine their potential applications in low earth orbit. In this study, a clear poly(amic acid) with an empirical 20 wt% polyhedral oligomeric silsesquioxane (POSS) solid content is designed for transparency and AO durability. Red, green, blue, and yellow dyes are reinforced with small amounts of 1–5 wt% in POSS polyimides for color filters. A silver nanowire network film is infiltrated onto the POSS polyimide for conductive film. Erosion depth upon hyperthermal AO exposure, surface morphology, surface chemistry, optical transparency, and conductivity have been systematically investigated. The erosion yields of all 20 wt% POSS polyimides decrease by an order of magnitude when subjected to 2.32 ± 0.05 and 2.39 ± 0.06 × 1020 atoms cm−2 AO fluences, as passivating SiOx networks are formed on film surface. The small‐amount dye additives into polyimides do not introduce obvious changes in AO durability and surface chemistry. The silver nanowire infiltrated POSS polyimide film shows a 65.7% transmittance at 550 nm and a sheet resistance of 8.50 ± 0.36 Ohm square−1. This study reveals promising attempts of POSS‐polyimide‐based color filters and flexible conductive films for potential space applications. [ABSTRACT FROM AUTHOR]

In this paper, relative orbit and attitude adaptive controllers are integrated to perform roto-translational maneuvers for CubeSats equipped with a Drag Maneuvering Device (DMD). The DMD enables the host CubeSat with modulation of aerodynamic forces/torques and gravity gradient torque. Adaptive controllers for independent orbital and attitude maneuvers are revisited to account for traslational-attitude coupling while compensating for uncertainty in parameters such as atmospheric density, drag/lift coefficients, location of the Center of Mass (CoM) and inertia matrix. Uniformly ultimately bounded convergence of the attitude error and relative orbit states is guaranteed by Lyapunov-based stability analysis for the integrated roto-translational maneuver. A simulation example of an along-track formation maneuver between two CubeSats with simultaneous attitude control using only environmental forces and torques is presented to validate the controller. [ABSTRACT FROM AUTHOR]

The selection of orbit propagation models strongly affects various space situational awareness applications like future object population prediction, collision avoidance maneuvers, object detection, object tracking, and catalog maintenance. Two key considerations in the selection of orbit propagation models are accuracy and computational cost. While one can use accurate numerical orbit propagation techniques for short propagation periods, it can be computationally taxing when the propagation period is long and/or when a large number of objects are to be propagated. This can be remedied by using analytical orbit propagation techniques, which not only facilitate fast orbit propagation but also permit meaningful theoretical insight into the structure of the perturbations. Most previous analytical object propagation in the near-Earth realm has been carried out in the presence of zonal and tesseral harmonics of Earth's gravity, Sun and Moon gravities, atmospheric drag, and solar radiation pressure. However, for high-energy plasma weather and under eclipse where objects can get highly charged, Lorentz force should be included for better accuracy in orbital propagation. Lorentz force should also not be ignored for high-area-to-mass ratio objects. Among the work that has taken Lorentz force into consideration, most have made the simplifying assumption of non-tilted Earth magnetic dipole or have developed analytical formulas valid only for low Earth orbit region. In this paper, new analytical formulas for Lorentz perturbations are developed using a tilted dipole Earth magnetic field and a constant charge-to-mass ratio. The derived analytical formulas are valid for all near-Earth altitudes. Two sets of formulas are derived, one for small eccentricities and one for large eccentricities. The analytical results are validated using numerical simulations. A comparative study is also carried out using different charging levels and area-to-mass ratios for the low Earth orbit and geosynchronous Earth orbit regions. • New analytical formulas for Lorentz perturbations for all near-Earth altitudes. • Lorentz force important for long propagation periods or HAMR objects. • Lorentz force modeling crucial for large voltage scenarios. [ABSTRACT FROM AUTHOR]

Summary: Due to the significant utilization of terrestrial communication, Low Earth Orbit (LEO) satellite network is a critical part of satellite communication networks owing to its several benefits. But the efficient and trustworthy routing for LEO satellite networks (LSNs) is a difficult process because of dynamic topology, adequate link changes, and imbalanced communication load. This study devises a new hybridization of extreme learning machine (ELM) with multitask beetle antennae search (MBAS) algorithm‐based distributed routing called the MBAS‐ELM model. The proposed model determines the routes based on traffic forecasting with respect to the level of traffic circulation on the earth. The proposed method is employed for traffic forecasting at the satellite nodes (SNs). To identify the optimal routes, mobile agents (MAs) are applied to concurrently and autonomously determine for LSNs and make a decision on routing data. The experimental outcome has showcased the effective performance of the proposed model over the compared models in terms of different measures, namely, average delay, packet loss ratio (PLR), and queuing delay. The results are validated under varying simulation time and data sensing rates. The obtained outcome pointed out the superior performance of the proposed MBAS‐ELM model compared with other methods. [ABSTRACT FROM AUTHOR]

Since Low Earth Orbit has become a popular orbit to place satellites, CubeSat constellation tracking is challenging. The higher capacity and capability of a new Ground Station tracking system are in demand and this motivates researchers to come out with a solution to mitigate the traditional Ground Station degradation performance. This paper discusses the implementation of the Least Mean Square algorithm to the Adaptive Array Antenna for the Ground Station tracking system application. The simulation results show the main beam pattern's capability to perform instantaneous tracking and steering towards the targeted CubeSat while suppressing the side lobes towards the other interfering CubeSats when massive CubeSats constellations take place. Planar and circular array antennas are analyzed by setting the optimum weighting factors to be adapted. Three scenarios of CubeSats constellations are simulated. The Adaptive Array Antenna's performance for each scenario is analyzed based on the beam width characteristics and the Signal-to-Interference Ratio of the beam pattern. The number of CubeSats tracked by the Adaptive Array Antenna and the system's capability to perform fast tracking as the number of antenna array elements is also discussed in this paper. Finally, solutions to mitigate the Least Mean Square algorithm's limitation to perform fast tracking when massive interferer CubeSats are nearby are proposed. [ABSTRACT FROM AUTHOR]

Thermospheric mass density (TMD) measurements are invaluable to accurately estimate and predict the position and velocity of orbiting objects in Low Earth Orbit (LEO). Existing observational methods and predictive models have some problems (e.g., accuracy, resolution, coverage, cost, etc.) to describe and forecast the actual air drag variations as required for practical applications. With the increasing number of LEO satellites equipped with high‐precision Global Navigation Satellite System (GNSS) receivers, the precise orbits can be used to obtain non‐gravitational accelerations, and therefore estimate TMD variations. In this study, TMD is estimated from the precise orbits of CAScade SmallSat and IOnospheric Polar Explorer (CASSIOPE) at one‐second time step, and the TMD variations following the February 2014 geomagnetic storm are investigated. Using this method, a more detailed description than previous methods and empirical models is given with short‐term TMD variations during geomagnetic storm conditions. The empirical model NRLMSISE‐00 shows less pronounced and more averaged variations, while CASSIOPE‐derived TMD can reflect the abrupt disturbances triggered by the geomagnetic storm. CASSIOPE TMD shows a correlation of 72.4% to the merging electric field Em index, while the NRLMSISE‐00 model shows a correlation of 42.1%. Key Points: Thermospheric mass densities are estimated from CAScade SmallSat and IOnospheric Polar Explorer precise orbitsThe detailed thermospheric mass density responses are obtained during the February 2014 geomagnetic stormCASSIOPE‐derived thermospheric mass density is better than the NRLMSIS‐00 model to reflect responses to the storm [ABSTRACT FROM AUTHOR]

In recent years, the multi-GNSS positioning application is becoming more and more popular, same to the low Earth orbit (LEO) satellite precise orbit determination (POD) based on the onboard multi-GNSS measurements. The third-generation Beidou navigation satellite system (BDS-3) provides a new option to obtain the LEO satellite orbit solutions. However, the receiver intersystem bias (ISB) of different GNSS is unavoidable in multi-GNSS data processing. This paper’s main goal is absorption of the impact of the ISB between BDS-3 and BDS-2 on the LEO satellite POD. Taking GPS-based POD solutions for the reference orbit, this paper evaluates the orbit accuracy of BDS-2-based POD, BDS-3-based POD, BDS-2 and BDS-3 combined PODs with/without ISB. The BDS-3-based POD accuracy is 6.57 cm in the 3D direction, a 56% improvement over BDS-2-based POD. When the ISB between BDS-3 and BDS-2 is estimated, the BDS-2/3 combined POD accuracy of 5.37 cm in the 3D direction is better than that without ISB, which is a 64% improvement over BDS-2-based POD and 18% improvement over BDS-3-based POD. For GPS and BDS-2/3 combined POD, the GPS and BDS-3 joint POD solutions have the smallest RMS differences in overlapping consistency and smallest RMS differences compared to GPS-based POD. This study indicates that estimating the BDS-2/3 receiver ISB in BDS-2/3 joint POD could improve the orbit accuracy, and the GPS and BDS-3 joint POD solution is better than another combined POD. This paper will provide meaningful references for the LEO satellite multi-GNSS-based POD.

TURKSAT-3USAT is the first Turkish communication 3U CubeSat designed and built by the students of the Space Systems Design and Test Laboratory and Radio Frequency Electronics Laboratory of Istanbul Technical University (ITU). Students partnered with TURKSAT, A.S. Company as well as the Turkish Amateur Technology Organization, when creating the design. The payload of TURKSAT-3USAT, having dimensions of 10 × 10 × 34 cm3, is an amateur band VHF/UHF transponder that will be used for voice communication. In this study, a thermal control system of TURKSAT-3USAT at 680 km altitude was presented. TURKSAT-3USAT used both passive and active thermal control. The thermal model of CubeSat was constructed and analyzed using ThermXL and ESATAN-TMS thermal analysis tools. The temperature results showed that all electronic components were within their allowed temperature range, except the batteries. For batteries, heaters are recommended during the cold case condition. Thermal cycling and bake-out testing were carried out on the flight model in a thermal vacuum chamber. [ABSTRACT FROM AUTHOR]

Satellite-based quantum key distribution is the key to develop the intercontinental quantum network. After the demonstrations by Chinese satellite Micius, the prospect of global-scale quantum internet is no more out of reach. However, the research efforts on modeling of constellation of quantum satellite is still insufficient so far. In this paper, we study the algorithm to select quantum key distribution access, the key size re-distribution optimization model and corresponding key size consumption along inter-satellite links. Besides, we present the brief discussion of how the constellation configuration interferes quantum key distribution performance. • A model for quantum key distribution (QKD) constellation based on communication window, which is divided into three optimization problem. • Modeling for quantum keys re-distribution. • Modeling for keys consumptions on inter-satellite links. • An algorithm to choose communication windows is proposed to significantly reduce difficulty of solving. [ABSTRACT FROM AUTHOR]

When CubeSat projects are a useful means by which universities can engage their students in space-related activities. TURKSAT-3USAT is a three-unit amateur radio CubeSat jointly developed by the Space Systems Design and Test Laboratory and the Radio Frequency Electronics Laboratory of Istanbul Technical University (ITU), in collaboration with TURKSAT, A.S. company as well as the Turkish Amateur Technology Organization. It was launched on April 26, 2013 as a secondary payload on a CZ-2D rocket from China's Jiuquan Space Center to an altitude of approximately 680 km. The mission of the satellite has two primary goals: (1) to voice communication at Low Earth Orbit (LEO) and (2) to educate students by providing hands-on experience. TURKSAT-3USAT was designed to sustain a circular, near sun-synchronous LEO, and has dimensions of 10 x 10 x 34 cm3. Within the course of this paper, TURKSAT-3USAT's thermal control will be addressed. TURKSAT-3USAT's thermal control model was developed using ThermXL and ESATAN-TMS software. Using this model, temperature distributions of the CubeSat when subjected to various experimental conditions of interest were computed. Using a thermal vacuum chamber (TVAC), thermal cycling and bake-out testing were carried out on the flight model to verify the thermal design performance and check the mathematical model. Based on thermal analysis results, the temperature of equipment was within the allowable temperature range except for the batteries that were between 42.56 oC and -20.31 oC. Heaters were used for the batteries in order to maintain the batteries' temperature within the allowable temperature range. [ABSTRACT FROM AUTHOR]

The emergence of the construction and operation of a small satellite constellation in Low Earth orbit (LEO) to beam high-speed Internet to all parts of the world is a relatively new development in the use of outer space. States, international intergovernmental organizations, and private companies plan to deploy small satellites into Earth's orbit because this effort is inexpensive and expandable, especially in the area of commercial activities. This movement will provide an essential tool to achieve sustainable development goals, especially for developing countries. However, it could also bring legal challenges because there is now a lack of binding regulations regarding the increasing risks of orbital collision, the proliferation of space debris, the satellite network service, and the rational, efficient, and economical use of a radio frequency allocation and the harmful interference caused by small satellite constellations in LEO. These issues could have an impact on the long-term sustainability of space activities. [ABSTRACT FROM AUTHOR]

In all links involving communications satellites, the aim is to send the best-quality signal with the lowest bandwidth and power using the simplest and most appropriate hardware. This is for everyone’s benefit, because it is necessary to satisfy enormous demands for all types of communications. For the purpose of achieving these targets, the design of communications-satellite systems is being shifted from the geostationary orbit to lower Earth orbits, where the best quality signal is achieved by minimizing the probability of error and latency. In a small-satellite constellation system, the design minimizes the complexity and the cost of implementing the proposed system, reduces the required transmission power, which translates into signal-to-noise ratio, and narrows the frequency spectrum being used. The work evaluates the Starlink-satellite broadband communications network developed by the American company SpaceX. The main technical characteristics of this special segment of broadband-communications networking based on the constellation network of small-satellite technology are reviewed and commented on. The main purpose of the paper is to clearly show the technical characteristics of the Starlink network that SpaceX does not disclose in popular-science presentations. [ABSTRACT FROM AUTHOR]

Summary: A major problem for low Earth orbit (LEO) constellations with intersatellite links is the efficient routing of the data packets through such a highly dynamic network. In order to achieve a worldwide coverage even in remote areas and Internet access with a limited amount of gateway stations, intersatellite links are a promising approach. Since LEO constellations represent a distinct, highly dynamic routing environment, specific strategies are needed. To this end, a suitable geographical routing scheme is proposed and investigated in two Walker Star constellations. The proposed scheme targets reliable transmissions with low latency and high data rates. The approach is based on a geographical address identifier in Layer 2 of the communication stack. The globe is thus divided into geographical areas that determine this identifier in the MAC address of the terminals. As mobile terminals are considered, the MAC addressing scheme is flexible, whereas the IP addresses of the terminals remain static. This decoupling allows for flexibility in the choice of the address resolution scheme. Moreover, the geographical identifier in the MAC address enables fast routing table lookups and switching. The proposed routing scheme also takes possible overloads of the satellites due to traffic into account and applies a rerouting procedure. When a packet arrives in the geographical area of the destination terminal, a local rerouting scheme is applied if needed. The proposed approaches take handover events that possibly occur during a transmission into account. Furthermore, the scan angles of the satellites have been adapted to the constellations to provide full coverage and high elevation angles. So a robust and adaptable routing scheme is provided for a dynamic environment where satellites and terminals are constantly moving. The proposed definitions and procedures have been implemented in a system level simulator, which allows for comparisons with adjustable parameters in various scenarios. In this work, an Iridium‐like constellation and a megaconstellation are investigated and compared regarding the address resolution procedures, the average end‐to‐end transmission delay, and the dropping and rerouting rates. Additionally, the signaling overhead is compared with other approaches. The simulator and results of the simulations provide grounds for further research w.r.t. the routing in satellite constellations using intersatellite links. [ABSTRACT FROM AUTHOR]

Copyright of Revista Ciencia y Poder Aéreo is the property of Escuela de Postgrados de la Fuerza Aerea Colombiana and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This research studies the orbital dynamics of space debris in near-earth orbit and calculates its respective lifetime. The orbital dynamics of space debris is closely examined in near-earth orbit whereby (apogee altitude ha=1200 km and perigee altitude hp=200 km). In addition, the lifetime of the space debris is calculated using the influence of the friction force exerted on the atmospheric particles with debris dimensions measuring between (1-10 cm). In this study, the Drag Thermospheric Models (DTM78 and DTM94) are used because of their dependence on solar and geomagnetic activities, and pulsed lasers are utilized to interact with Aluminum 2024 particles which are frequently employed in the structure of spacecraft and aerospace designs. A numerical analysis program (NaP1) was built to calculate the lifetime of space debris and its time of return to the atmosphere. It is then integrated with a second numerical analysis program (NaP2) developed using the Lax-Wendroff finite difference method to simulate the laser material interaction model. A high-power Nd:YAG laser was applied to produce shock wave pressure in the target. The results show that the maximum peak pressure occurs at 50 μm depth and then slowly decays, the peak pressure increases with the increase of the laser intensity, and the optimum value of the momentum coupling coefficient (Cm) for the aluminum debris of size range (1-10 cm) is 6.5 dyn.s/j.

This study concerns in addressing the lifetime and reentry of the space debris in LEO which extends from 200 to 1200 km. In this study the new Computer programs are designed to simulate orbit dynamics of space debris lifetime and reentry under atmospheric drag force by using Runge-Kutta Method to solve the differential equations of drag force and this model was adapted with the Drag Thermosphere Model (DTM78, 94), the Aluminum 2024 space debris in certain size (1-10 cm) were used in this study, which is frequently employed in the structure of spacecraft and aerospace designs. The selected atmospheric model for this investigation is the drag thermospheric models DTM78 and DTM94, because of this dependence on solar and geomagnetic activities. It has been found that the lifetime of the space debris increases with increasing perigee altitudes. It has been found that the elliptical shape of the debris orbit would change gradually into a circular shape, then its kinetic energy would be transformed into heat and hence debris destroy in the dense atmosphere.

The real-time integer-ambiguity resolution of the carrier-phase observation is one of the most effective approaches to enhance the accuracy of real-time precise point positioning (PPP), kinematic precise orbit determination (KPOD), and reduced-dynamic precise orbit determination (RPOD) for low earth orbit (LEO) satellites. In this study, the integer phase clock (IPC) and wide-lane satellite bias (WSB) products from CNES (Centre National d’Etudes Spatiales) are used to fix ambiguity in real time. Meanwhile, the three models of real-time PPP, KPOD, and RPOD are applied to validate the contribution of ambiguity resolution. Experimental results show that (1) the average positioning accuracy of IGS stations for ambiguity-fixed solutions is improved from about 7.14 to 5.91 cm, with an improvement of around 17% compared to the real-time float PPP solutions, with enhancement in the east-west direction particularly significant, with an improvement of about 29%; (2) the average accuracy of the estimated LEO orbit with ambiguity-fixed solutions in the real-time KPOD and RPOD mode is improved by about 16% and 10%, respectively, with respect to the corresponding mode with the ambiguity-float solutions; (3) the performance of real-time LEO RPOD is better than that of the corresponding KPOD, regardless of fixed- or float-ambiguity solutions. Moreover, the average ambiguity-fixed ratio can reach more than 90% in real-time PPP, KPOD, and RPOD.

The problems of delivery of small space vehicles into low earth orbits are pointed out. The up-to-date means for the ascent of small space vehicles into low earth orbits are analysed. The solution for responsive and economical ascent of small space vehicles into low earth orbits in the form of "MARKS" small aviationrocket space launch system is offered. Implementation of the offered idea will provide the price of delivery of 1 kg payload into 500 km sun-synchronous orbit equal to 3750 US dollars.

Copyright of Journal of Kufa - Physics is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Kufa - Physics is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The cold start of the space GPS receiver, i.e. the start without any information about the receiver position, satellite constellation, and time, is complicated by a large Doppler shift of a navigation signal caused by the satellite movement on the Earth orbit. That increases about five times the search space of the navigation signals compared to the standard GPS receiver. The paper investigates a method of the acceleration of the GPS receiver cold start time designed for the pico- and femto-satellites. The proposed method is based on a combination of the parallel search in Doppler frequency and PRN codes and the serial search in code phase delay. It can shorten the cold start time of the GPS receiver operating on LEO orbit from about 300 to 60 seconds while keeping the simplicity of FPGA signal processor and low power consumption. The developed algorithm was successfully implemented and tested in the piNAV GPS receiver. The energy required for the obtaining of the position fix was reduced five times from 36 on to 7.7 Joules. This improvement enables applications of such receiver for the position determination in smaller satellites like Pocket Cube or femto-satellites with a lower energy budget than the Cube Satellite. [ABSTRACT FROM AUTHOR]

Copyright of Military Science Review / Hadtudományi Szemle is the property of National University of Public Service and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The ReDSHIFT H2020 European project has shown, among other findings, that passive disposal procedures can benefit from the exploitation of dynamical perturbations. One key aspect of the project was a study on the dynamical disposal of spacecraft at the end-of-life by exploiting natural perturbations and identifying stable and unstable regions in the phase space, where the objects could be moved to exploit either long term "graveyards" or, possibly and preferentially, faster escape routes (the so-called "de-orbiting highways"). In particular, for the Low Earth Orbit (LEO) region, a natural eccentricity growth can be leveraged in order to reenter to the Earth's atmosphere at a lower Δv-budget. The numerical cartography of the region has been proven from a theoretical perspective, on the basis of a frequency analysis focused on solar radiation pressure and lunisolar perturbations and on dynamical systems theory tools. In this work, we summarize the whole study concerning the dynamics that characterizes the LEO region in the long-term, by giving a comprehensive picture of the theoretical findings together with their possible exploitation for the debris mitigation. The efficiency of the "de-orbiting highways" is tested and validated with a "thought experiment" by means of long-term propagation of a population of objects stemming from a specific traffic launch. It is shown how the de-orbiting corridors could be very effective in removing the majority of objects from the high LEO region at the end-of-life, thus contributing to the stabilization of the space debris environment, in particular for high-altitude spacecraft. • Identification of the main solar radiation pressure resonances in Low Earth Orbit. • Exploitation of the resonances (resonant corridors) for the dynamical disposal of objects at the end-of-life. • Simulations showing the effectiveness of the resonant corridors for the stabilization of the space debris environment. [ABSTRACT FROM AUTHOR]

In this paper, austenitic EN-1.4404—AISI 316L stainless steel assemblies have been brazed using concentrated solar energy, in vacuum, air and argon media, under different heating and cooling conditions. A nickel-based alloy (EN 2.4360—Monel 400) has been used as a filler material for brazing, aiming to obtain mechanically and chemically resistant joints, with potential application in low Earth orbit assembling where the solar energy flux bears higher values and degradative conditions are more demanding. By brazing with Monel in vacuum, good quality joints were obtained with minimal defects, being composed of solid solution grains, with shear strength values of 285–320 MPa and elongation values of 4.5–6 mm, while in argon medium, shear strength values of 350–370 MPa and elongation values of 7–8 mm have been obtained. Concentrated solar energy brazing in vacuum and argon has led to promising results which could prove an alternative to on-site low Earth orbit construction joining. [ABSTRACT FROM AUTHOR]

Satellites must endure the hostile environement during their launching to space via rocket; therefore, they should be exposed to the real launch conditions for ground testing, including all subsystems and components which should be carefully tested. Several solid-stateceramic batteries have been selected to be evaluated under the launch environment after been evaluated under the space environment, which has shown so far good results. This paper focuses on the physical degradation and the electrical performances of the batteries based on the discharge capacity, the open-circuit voltage, and charge/discharge modes. Batteries have been exposed to shock, then tested under vibration within different frequencies' levels with sinewave, sine burst, and random. Before and after the test, the physical properties of all batteries have been checked, several cycles of discharge and charge have been performed to check their performances and survivability after the evaluation test. With 95% of capacity, batteries could demonstrate their ability to withstand the launch conditions successfully, they could be able to operate during several cycles after the test, so far, showing no degradation on their performances within the limits. Also, the paper is providing the main requirements and criteria for batteries' launch ground testing for the small satellite project. [ABSTRACT FROM AUTHOR]

This article presents the conceptual design of a three-stage rocket to carry 200 kg payload to low Earth orbits (by the acronym LEO). From a case study of the fight path of a three-stage rocket with solid propellants, proceed to select the propellant mixture that meets the design requirements and path raised fight, taking into account that it can produce nationwide. The propellant thermochemical behavior is obtained with CPROPEP software. Knowing the values of pressure, temperature and specific heat ratio in the combustion chamber proceeds to design rocket engines to ensure total velocity change in the system equivalent to those obtained in the analysis of the fight path. With the design of the propulsion duct materials that withstand the thermal loads and pressure, to give way to structural design giving an approximation of carrier rocket are chosen. [ABSTRACT FROM AUTHOR]

Spacecraft operating in low-Earth orbit are subjected to a number of hazardous environmental constituents that can lead to decreased system performance and reduced operational lifetimes. Due to their thermal, optical, and mechanical properties, polymers are used extensively in space systems; however they are particularly susceptible to material erosion and degradation as a result of exposure to the LEO environment. The focus of this research is to examine the material erosion and mass loss experienced by a custom Kapton-like polyimide due to exposure in a simulated low-earth orbit environment. The deployable membrane telescope design discussed in this research is named Peregrine and is the scientific payload for FalconSat-7, a 3U cubesat designed and developed at the United States Air Force Academy (USAFA) for the purpose of demonstrating the capability of deployable membrane telescope technology on a nano-satellite platform. In addition to the polymer samples, chrome, silver and gold specimens will be examined to measure the oxidation rate and act as a control specimen, respectively. A magnetically filtered atomic oxygen plasma source has previously been developed and characterized for the purpose of simulating the low-Earth orbit environment. The plasma source can be operated at a variety of discharge currents and gas flow rates, of which the plasma parameters downstream of the source are dependent. The characteristics of the generated plasma were examined as a function of these operating parameters to optimize the production of O+ ions with energy relevant to LEO applications. The erosion yield of the Kapton-like polyimide was experimentally determined to be 2.84 × 10−24 cm3 per atom which is in close agreement when compared to the on-orbit measurement for reaction efficiency of Kapton HN. The experimentally determined reaction rate for the Kapton-like polyimide was used to estimate the operational lifetime of the photon sieve during the solar conditions expected beginning in May 2019. The effective lifetime is estimated between 126 and 153 days. [ABSTRACT FROM AUTHOR]

A specific criticality index, the collision rate percentage increase, was introduced in 2017 to assess the environmental impact of large satellite constellations in low Earth orbit (LEO). That index was estimated in this paper for various constellation arrangements, ranging in altitude from 800 km to 1400 km. The results obtained clearly show that in the regions of space where the current density of cataloged debris is already significant, such as around 800 km, just one hundred more abandoned satellites would increase the current collision rate by ~10%. In less congested LEO regions, as near 1110 km and 1325 km, a comparable increase in the collision rate could be achieved by a number of abandoned satellites between 200 and 500. Taking into account the new planned constellations from 800 km to 1400 km (consisting of approximately 6000 satellites), an increase by nearly 20–30% of the total collision rate among cataloged objects in LEO might be expected, assuming an immediate spacecraft de-orbiting at the end-of-life, with a success probability of 90%. Of course, a greater number of satellites, as well as a reduced probability of successful disposal, would affect the environment even more negatively. Moreover, if the many disposed satellites were not de-orbited immediately, or in a relatively short time, the collision rate in LEO would further increase, at least in the medium term, unless the satellites do not continue to be controlled and maneuverable until they reenter the atmosphere. As an example, if a thousand satellites were disposed on elliptical orbits between 300 km and 1000 km, the collision rate among cataloged objects in LEO might grow by an additional 30% during the few years needed to decay. That said, even assuming a willingness to endure a maximum 50% increase in the collision rate in LEO among objects greater than 10 cm, in the next 25 years, it is clear that an extended and expanded use of large constellations would be consistent with the environment sustainability only if it were possible to increase the post-mission disposal success probability to at least 95%, and hopefully to 99%. At the same time, the de-orbiting phase should be either quite short or fully controlled, in order to avoid the prolonged presence of several hundred or thousands of abandoned satellites in disposal orbits, further increasing the collision rate in low LEO. • The collision rate percentage increase CRI among cataloged objects was defined. • CRI was estimated for various large constellations, from 800 km to 1400 km. • Around 800 km, ~100 more failed spacecraft would increase the current CRI by 10%. • In less crowded regions, a 10% increase would be caused by 200–500 lost spacecraft. • The overall CRI increase would be 20–30% with a successful disposal rate of 90%. [ABSTRACT FROM AUTHOR]

The desired capabilities of small satellites to enable their applications in communication, earth observation, and new scientific instruments require advanced energy storage to face the design's challenges with the constraints of volume and mass. Small batteries with high energy density may be the solution. New lithium-ion battery technologies areimproved in order to meet these requirements by bringing higher energy density and a wide temperature range than the commercially available ones as well as a lower risk of explosion. In this paper, the ability of solid-state-ceramic batteries to withstand the vacuum and thermal vacuum for low earth orbit applications has been demonstrated, with a minimum safety issue. So far, this technology has never been flown in space. This paper also provides a guideline for the battery evaluation test where the main lines are represented. Batteries are tested under vacuum and thermal vacuum, where they are discharged and charged during several cycles between two temperatures limits. The evaluation focuses on analyzing the physical degradation, the discharge capacity, and the internal resistance before and after each test. Batteries have showed promising results regarding their survivability to thermal vacuum. After several cycles, they have kept almost the same performances, with the same internal resistance and 98% of capacity. [ABSTRACT FROM AUTHOR]

Groups of carbon/carbon (C/C) and tantalum carbide (TaC)-coated C/C composite specimens were studied under exposure to atomic oxygen (AO). Low earth orbit ground-based simulator was employed. Degradation mechanisms were investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, and energy dispersive spectrometry. The results indicated that compared to C/C composite, TaC-coated C/C composite exhibited improvements in resistance properties against AO flux, such as 16.7% better strength retention ratio and 57% less mass ablation than non-coated C/C after 40 h of AO exposure. Moreover, AO preferentially consumed tantalum (Ta) atoms than carbon atoms of TaC x till atomic ratio was in the same proportion. Production of swollen tantalum oxide and crack healing components were obtained under the oxidation effect of high-speed AO. Swelling textures due to exposure were developed following an apical dominance growth behavior. The damage mechanisms of AO on TaC-coated C/C were revealed as chemical reaction first followed by mechanical effect. [ABSTRACT FROM AUTHOR]

Zirconium carbide (ZrC) components were induced as coating modification on carbon/carbon (C/C). These ZrC–C/C specimens were investigated after atomic oxygen (AO) exposure for different assessment times, low earth orbit (LEO) ground-based environmental simulator was employed. The results indicate that ZrO 2 is the major production generated by the AO chemical reaction with the ZrC coating. Upon further exposure to AO, the production of ZrO 2 would drop off, then exfoliate easily, due to the mechanical impacting effect. Then the exposed graphite matrix and carbon fiber get corroded. Amorphous diamond-like carbon (DLC) is detected by X-ray photoelectron spectroscopy during AO exposure. Bending strength performance increased by 25% under AO exposure at first 10 h, then dropped by 52.1% from 10 h to 30 h of AO exposure. The AO damage mechanisms of ZrC–C/C composites are revealed. [ABSTRACT FROM AUTHOR]

In this paper, the repeat-groundtrack orbit maintenance problem is addressed for spacecraft driven by electric propulsion. An adaptive solution is proposed, which combines a hysteresis controller and a recursive least squares filter. The controller provides a pulse-width modulated command to the thruster, in compliance with the peculiarities of the electric propulsion technology. The filter takes care of estimating a set of environmental disturbance parameters, from inertial position and velocity measurements. The resulting control scheme is able to compensate for the groundtrack drift due to atmospheric drag, in a fully autonomous manner. A numerical study of a low Earth orbit mission confirms the effectiveness of the proposed method. • A novel low-thrust repeat-groundtrack orbit maintenance scheme is devised. • The control scheme is able to adapt to unknown environmental disturbances. • A low-Earth-orbit mission case study demonstrates the effectiveness of the method. [ABSTRACT FROM AUTHOR]

The evolution of the solar system and the origin of life remain some of the most intriguing questions for humankind. Addressing these questions experimentally is challenging due to the difficulty of mimicking environmental conditions representative for Early Earth and/or space conditions in general in ground-based laboratories. Performing experiments directly in space offers the great chance to overcome some of these obstacles and to possibly find answers to these questions. Exposure platforms in Low Earth Orbit (LEO) with the possibility for long-duration solar exposure are ideal for investigating the effects of solar and cosmic radiation on various biological and non-biological samples. Up to now, the Exobiology and space science research community has successfully made use of the International Space Station (ISS) via the EXPOSE facility to expose samples to the space environment with subsequent analyses after return to Earth. The emerging small and nanosatellite market represents another opportunity for astrobiology research as proven by the robotic O/OREOS mission, where samples were monitored in-situ , i.e. in Earth orbit. In this framework, the European Space Agency is developing a novel Exobiology facility outside the ISS. The new platform, which can host up to four different experiments, will combine the advantages of the ISS (long-term exposure, sample return capability) with near-real-time in-situ monitoring of the chemical/biological evolution in space. In particular, ultraviolet–visible (UV–Vis) and infrared (IR) spectroscopy were considered as key non-invasive methods to analyse the samples in situ. Changes in the absorption spectra of the samples developing over time will reveal the chemical consequences of exposure to solar radiation. Simultaneously, spectroscopy provides information on the growth rate or metabolic activities of biological cultures. The first quartet of experiments to be performed on-board consists of IceCold, OREOcube and Exocube (dual payload consisting of ExocubeChem and ExocubeBio). To prepare for the development of the Exobiology facility, ground units of the UV–Vis and IR spectrometers were studied, manufactured and tested as precursors of the flight units. The activity led to a modular in-situ spectroscopy platform able to perform different measurements (e.g. absorbance, optical density, fluorescence measurements) at the same time on different samples. We describe here the main features of the ground model platform, the verification steps, results and approach followed in the customization of commercial–off-the-shelf (COTS) modules to make them suitable for the space environment. The environmental tests included random and shock vibration, thermal vacuum cycles in the range −20 °C to +40 °C and irradiation of the components with a total dose of 1800 rad (18 Gy). The results of the test campaign consolidated the selection of the optical devices for the Exobiology Facility. The spectroscopic performance of the optical layout was tested and benchmarked in comparison with state-of-the-art laboratory equipment and calibration standards showing good correlation. This includes spectra of samples sets relevant for the flight experiments and a performance comparison between the SPECTROModule ground model and state-of-the-art laboratory spectrometers. Considering the large number of samples and different types of optical measurements planned on-board the ISS, the main outcome was the implementation of an LED-photodiode layout for the optical density and fluorescence measurements of IceCold (42 samples) and ExocubeBio (111 samples); while the UV–Vis spectrometer will be mainly focused on the change of the absorption spectra of the 48 samples of OREOcube.The ExocubeChem samples (in total 48) will be analysed by infrared spectroscopy. The ground platform supports the establishment of analogue research capabilities able to address the long-term objectives beyond the current application. • Biological samples shall be exposed to solar and cosmic radiation. • UV/VIS and IR spectroscopy are used for in-situ measurements in space. • Commercial off-the shelf (COTS) spectrometers were tested and verified for use in space. • A scientific test campaign proved the predicted results. • SPECTROmodule is the precursor mission of the Exobiology facility accommodated outside the International Space Station. [ABSTRACT FROM AUTHOR]

In the article, the authors considered the challenges for space law, which are created by the intensive development of production technologies of unmanned spacecrafts and space drones, as well as their use in the space industry. The authors clarified the term "space object", which is used in the Space Law. This helped reveal the difference between the terms "unmanned spacecrafts" and "space drones", which are synonymous in the Air Law. The authors investigated the basics of the space law and proved that in the existing formulations, the space law is not able to regulate the modern space exploration. Based on the study, the authors proposed: (1) to consolidate the influence of public organizations created in the space industry and specializing in the space exploration in the space law; (2) to change approaches to space law; space law should be considered as an effective regulator capable of ensuring the sustainable development of the mankind;. (3) under the space law, to create a holistic concept for using all types of space object on the Low Earth Orbit. [ABSTRACT FROM AUTHOR]

Other than traditional single-layer ionosphere models for global navigation satellite system (GNSS) receivers, the NeQuick-G model of Galileo provides a fully three-dimensional description of the electron density and obtains the ionospheric path delay by integration along the line of sight. While optimized for users on or near the surface of the earth, NeQuick-G can thus as well be used for ionospheric correction of single-frequency observations from spaceborne platforms. Based on slant and total electron content measurements obtained in the Swarm mission, the performance of NeQuick-G for users in low earth orbit is assessed for periods of high and low solar activity as well as different orientations of the orbital plane with respect to the sun and the region of high total electron content. A slant range correction performance of better than 70% is achieved in more than 85% of the examined epochs in good accord with the performance reported for terrestrial users. Likewise, the positioning errors can be notably reduced when applying the NeQuick-G corrections in single-frequency navigation solutions. For users at orbital altitudes, it is furthermore shown that vertical total electron predictions from NeQuick-G may be favorably combined with an elevation-dependent thick-layer mapping function to reduce the high computational effort associated with the integration of the electron density along the ray path for each tracked GNSS satellite. [ABSTRACT FROM AUTHOR]